The deal to reform the pensions of local government workers is being put at risk by "delays and confusion" over its implementation, a leading union has warned.

The GMB said draft regulations to introduce agreed changes to the scheme that were due at the end of September have not been issued. Proposals put forward by unions and employers at the end of July to manage the future costs of the scheme have received no response from the Government, said the GMB.

The Public Service Pensions Bill, which covers the reform of public-sector pensions, will receive its second reading in Parliament on Monday but the GMB said it was " incompatible" with the local government scheme.

GMB national officer Brian Strutton said: "The GMB and the other local government unions have worked really hard with council leaders to design benefit and cost changes to the Local Government Pension Scheme (LGPS) that will make it affordable and fair.

"However, government has been abysmally slow in responding to proposals and has so far failed to keep its side of the deal. For example, LGPS scheme members and employers voted convincingly to accept the reform package and government promised this would be put into draft regulation by the end of September."

Unions were involved in a long-running dispute with the Government over the reforms, which were eventually accepted by local government workers, but not by others, including civil servants and teachers.

The Public and Commercial Services union has pledged to continue opposing the reforms, saying public-sector staff were being told to pay more, receive less in retirement and work longer before receiving a pension.

General secretary Mark Serwotka said: "This is the Government's latest attempt to force through massive cuts to the pensions of tens of thousands of public servants from jobcentre staff to tax advisers and nurses to teachers, after refusing to negotiate on the central plans to force them to pay more every month and work up to 68 for much less in retirement.

"We remain committed to opposing this entirely unnecessary attack on pensions, which cannot be separated from the Government's politically-motivated cuts to pay and jobs and the latest threat to undermine all civil service working conditions, including hours, holidays and family-friendly policies."

A government spokesman said: "The Government's reforms to public service pensions will save around £430 billion over the next 50 years and are a good deal for taxpayers and public-service workers. Our objective is to keep public-service pensions amongst the very best available, with those on low and middle incomes receiving a pension at retirement least as good, if not better, than now."